Apparatus and method related to core-shell magnetic nanoparticles and structured nanoparticles

ABSTRACT

One aspect of the invention requires an apparatus for forming core-shell magnetic nanoparticles comprising: a magnetic nanoparticle source operable to generate a beam of nanoparticles; at least one shell material source comprising a bore through which the beam of nanoparticles may pass; and at least one controllable magnetic field generator, operable to generate a magnetic field which at least partially surrounds the at least one shell material source, wherein nanoparticles may be received at one end of the shell material source and the movement of the nanoparticles within the bore may be controlled by the controllable magnetic field to be coated by the shell material to specified dimensions, and nanoparticles may leave the other end of the shell material source. Another aspect of the in invention is a method of manufacturing core-shell magnetic nanoparticles, wherein: a beam of magnetic nanoparticles is generated by the nanoparticles source (34); and at least one vapour of at least one shell material is generated by at least one shell material source (36, 38, 50), wherein the at least one vapour of at least one shell material is located within the field generated by a controllable magnetic field generator (80); wherein the beam of nanoparticles enter the vapour of at least one shell material source (36, 38, 50) and the movement of the magnetic nanoparticles is controlled to coat the nanoparticles with the at least one shell material to specified dimensions and subsequently the coated nanoparticles are directed from the at least one shell material source to exit the at least one shell material source.

FIELD OF THE INVENTION

The present invention relates to the production of coated nanoparticlesfor deposition on a substrate. In particular, the invention is relatedto controlling the coating process and more precisely controlling thedimensions of the coat layer or layers. The material may be used in avariety of applications.

BACKGROUND TO THE INVENTION

Magnetic materials find widespread use in modern technology.Particularly, they are to be found in nearly all electro-mechanicalapparatus. The performance of magnetic materials in respect of theirsecondary parameters, such as coercivity and energy product, hasimproved greatly over the last century.

As shown in FIG. 1 a magnetic structure 10 may be formed byco-deposition on a substrate 12 of Fe nanoparticles 14 from a clustersource 16 and of Co matrix material 18 from a Molecular Beam Epitaxy(MBE) source 20. Co-deposition of Fe nanoparticles and Co matrixmaterial results in a structure in which Fe nanoparticles aredistributed through and embedded in the Co matrix. According to analternative approach a magnetic structure, in which Co nanoparticles aredistributed through and embedded in an Fe matrix, is formed byco-deposition of Co nanoparticles from the cluster source and of Fematrix material from the MBE source.

GB2530562B describes an apparatus for coating nanoparticles. Theapparatus aims to form a uniform coating on vaporised metalnanoparticles.

Nanoparticles are produced by vaporising a source of core material, in agas-phase environment. The nanoparticles are coated by passage through aplurality of shell evaporators. The shell evaporators comprise a heatedtube providing an elongate open channel. Shell material is locatedwithin the heated tube. The shell material is evaporated by the heatingthe tube and is deposited on the nanoparticles passing through the tube.Thus, a nanoparticle is produced comprising a core material coated in ashell material. The core-shell nanoparticle can be deposited on asubstrate.

The thickness of the shell layer may be controlled by varying theoperating conditions of the shell material source. The shell materialsource may be disposed between the source of nanoparticle cores and thesubstrate. In addition, the shell material source may be configured todefine a space through which a beam of nanoparticle cores pass, thesource being operative to form a vapour of shell material in the space,such that the vapour impinges upon a surface of each particle core. Theshell material source is configured to surround the beam of particlecores. The shell material source may, for example, define a bore or tubethrough which the beam of particle cores passes.

Thus, it is possible to produce magnetic core-shell nanoparticles wherethe core material is completely or substantially completely coated, forimproved electromagnetic properties.

According to the methods and apparatus described in the patents notedabove, the core nanoparticles are driven from the nanoparticle source tothe substrate by the atmosphere within the gas-phase environment.Typically the main driving force is a directional pressure differencecaused by the pump used to evacuate the equipment. Therefore, thedimensions of the shell layer on the core nanoparticles are determinedby variables such as the pump speed and the evaporation rate of theshell material in the heated tube. It will be apparent that while someof the parameters of the film deposition process may be controlled andvaried, control over the shell layer dimensions is relatively coarse andlimited.

It is difficult to control the shell layer or coating with muchprecision. With more control over the shell layer it will be possible tofurther exploit the properties of magnetic nanoparticles in existing andnew applications.

Therefore, if it were possible to control the dimensions or the shellmaterial more finely, it would be possible to provide magneticnanoparticles with electromagnetic properties which are also morerefined and have a better tolerance. It is the aim of the presentinvention to produce such nanoparticles using an apparatus and method asdisclosed herein.

SUMMARY OF INVENTION

Aspects of the invention are set out in the accompanying claims.

One aspect of the invention requires an apparatus for forming core-shellmagnetic nanoparticles comprising: a magnetic nanoparticle sourceoperable to generate a beam of nanoparticles; at least one shellmaterial source comprising a bore through which the beam ofnanoparticles may pass; and at least one controllable magnetic fieldgenerator, operable to generate a magnetic field which at leastpartially surrounds the at least one shell material source, whereinnanoparticles may be received at one end of the shell material sourceand the movement of the nanoparticles within the bore may be controlledby the controllable magnetic field to be coated by the shell material tospecified dimensions, and nanoparticles may leave the other end of theshell material source.

Another aspect of the invention is a method of manufacturing core-shellmagnetic nanoparticles, wherein: a beam of magnetic nanoparticles isgenerated by the nanoparticles source (34); and at least one vapour ofat least one shell material is generated by at least one shell materialsource (36, 38, 50), wherein the at least one vapour of at least oneshell material is located within the field generated by a controllablemagnetic field generator (80); wherein the beam of nanoparticles enterthe vapour of at least one shell material source (36, 38, 50) and themovement of the magnetic nanoparticles is controlled to coat thenanoparticles with the at least one shell material to specifieddimensions and subsequently the coated nanoparticles are directed fromthe at least one shell material source to exit the at least one shellmaterial source.

Another aspect of the invention requires an apparatus for formingstructure magnetic nanoparticles comprising: a nanoparticle sourceoperable to generate a beam of magnetic nanoparticles; and at least onecontrollable magnetic field generator, operable to generate a magneticfield through which the beam of nanoparticles may pass, whereinnanoparticles may be controlled when within the controllable magneticfield to be arranged into a specified structure of nanoparticles.

Another aspect of the invention is a method of manufacturing structurednanoparticles wherein: a beam of magnetic nanoparticles is generated bythe nanoparticles source (34) which passes through a field generated bya controllable magnetic field generator (80); wherein magneticnanoparticles are controlled within the controllable magnetic field tobuild structured nanoparticles.

Another aspect of the invention requires a core-shell magneticnanoparticle or a core-shell magnetic nanoparticle structure comprising:a magnetic core; and at least one shell layer having a layer thicknessof more than 4 nm.

Another aspect of the invention is the use of magnetic core-shellnanoparticles and or structured nanoparticles in hard disk driveapplications, medical applications and medical instruments, cosmetics,and or motor, generator or turbine applications.

Other aspects of the invention will become apparent from the followingdisclosure.

BRIEF DESCRIPTION OF DRAWINGS

In order that the present invention may be more readily understood,embodiments thereof will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 illustrates the formation of a magnetic structure;

FIG. 2 shows in block diagram form apparatus for forming a magneticstructure;

FIG. 3 shows apparatus for coating a core of a nanoparticle; and

FIG. 4 shows a nanoparticle having an Fe core, a first layer of Cr and asecond outer layer of a rare earth metal;

DETAILED DESCRIPTION OF THE INVENTION

It will be appreciated and understood that reference herein to magneticnanoparticle(s) or nanoparticle(s) refers to elemental nanoparticles,alloy nanoparticles or to magnetic core-shell nanoparticles.Nanoparticles may be defined as particles of material which are between0.5 nm and 50 nm in diameter.

Nanoparticles which are sometimes known as ‘simple nanoparticles’ referto uncoated nanoparticles. ‘Core-shell nanoparticles’ refers tonanoparticles which have a core comprising a ‘simple nanoparticle’ whichis coated in a shell of other material. ‘Multishell nanoparticles’ referto core-shell nanoparticles where two or more layers of shell materialhave been used to coat the core. Each of the multilayers may bedifferent materials, or shell materials may be repeated. Structurednanoparticles refer to structures constructed from a plurality ofnanoparticles. The plurality of nanoparticles which make up a structurednanoparticles may comprise simple nanoparticles, core-shellnanoparticles, multishell nanoparticles or any combination thereof.

Apparatus

FIG. 2 shows a block diagram of an apparatus 30 for forming an enhancedmagnetic structure. The apparatus 30 comprises a matrix material source32, a nanoparticle source 34, a first shell material source 36, and asecond shell material source 38. The matrix material source 32 may be,for example, a thermal evaporator device (such as an MBE device), asputtering device, a laser ablation device, or an arc device. Thenanoparticle source 34 may be, for example, a thermal evaporator device,a sputtering device, a laser ablation device, or an arc device. Thefirst and second shell material sources may be, for example, a thermalevaporator device, a sputtering device, a laser ablation device, or anarc device.

The apparatus 30 further comprises a temperature control apparatus 42which is operable to control the temperature of a substrate 44 and itsenvirons. The temperature control apparatus may make use of liquidnitrogen, or any other suitable technique. The nanoparticle source 34and the first and second shell material sources 36, 38 are preferablylocated in and operate in the same vacuum.

The matrix material source 32 is operable to generate a beam of matrixmaterial. The beam of matrix material may be an atomic beam, a molecularbeam, or a mixed beam, dependent upon the matrix material.

The nanoparticle source 34 is operable at the same time as the matrixmaterial source to generate a beam of nanoparticles. The two beams aredeposited simultaneously on the substrate 44 to form a magneticstructure in the form of a thin film matrix formed from deposited matrixmaterial with nanoparticles distributed through and embedded in thematrix.

The first and second shell material sources 36, 38 of FIG. 2 may be ofthe same type, or may be of different types, dependent upon the materialbeing deposited to form the respective shell layer.

FIG. 3 provides a schematic view of an exemplary shell material source50 of the type disclosed in GB2530562B.

The shell material source 50 of FIG. 3 is of generally tubular form suchthat it defines a bore through which a beam of nanoparticles may pass.The shell material source 50 preferably comprises a tube of purematerial 52 which is to be deposited as a layer on each of thenanoparticles passing through a thermal evaporator. The shell materialsource 50 further comprises a tubular heater 54 which surrounds and isadjacent the tube of pure material 52. A water cooled heat shield 56surrounds the outwardly directed surface of the tubular heater 54 andthe end faces of the tubular heater 54 and the tube of pure material 52.In use, the shell material source 50 operates to vaporise the purematerial 52 with the material vapour being present in the bore of thethermal evaporator. A beam of uncoated nanoparticles 58 is received atone end of the bore of the shell material source 50 and on passingthrough the material vapour in the bore the nanoparticles are coatedwith a layer of the material. The coated nanoparticles 60 then leave theother end of the bore of the shell material source 50.

In one example of the apparatus 30, nanoparticles are coated with onlyone layer of material, and the second shell material source 38 of theapparatus of FIG. 2 is either absent or inoperative.

In another example of the apparatus 30, nanoparticles are coated withfirst and second layers of the same or different material, and the firstshell material source 36, 50 comprises a tube of a first material 52 andthe second shell material source 38, 50 comprises a tube of the firstmaterial or a second different material 52.

In further examples of the apparatus 30, nanoparticles are coated withthird and further layers of the same or different material. Accordingly,such examples comprise shell material sources which correspond in numberto the number of layers to be deposited on the nanoparticles with theplural shell material source disposed in line such that the beam ofnanoparticles can pass in turn through the bore of each of the shellmaterial sources. The exact form of each of the shell material sourcesdepends upon the material being deposited.

The apparatus 30 further comprises a magnetic field generator 80. Themagnetic field generator is preferably located outside of the evacuatedenvironment, and in the example shown surrounds the shell materialsource(s) 36, 50. The magnetic field generator 80 may be coupled to andcontrolled by a programmable computer. The computer thereby controlswhen the field is generated by the magnetic field generator 80, theduration for which the field is generated, and the direction andstrength of the field. A computer program is used to activate generationof the magnetic field and vary the direction and strength of themagnetic over a period of time. For example, the magnetic field may bepulsed.

Typically, an electromagnetic coil or series of coils will be used togenerate a magnetic field.

In order to control the direction of the magnetic field, threesub-generators may be used. The sub-generators are arrangedorthogonally, or substantially orthogonally, to each other in order tocontrol the strength and direction of the magnetic field in threedimensional space.

There may be provided magnetic field generators 80, separatelycontrollable, for each of the shell material sources 36, 38, 50. In onearrangement, a single magnetic field may extend entirely or partiallyover one of the shell material sources 36, 38, 50. In anotherarrangement, a first magnetic field generated by a first magnetic fieldgenerator may cover a first end of a shell material source, and a secondmagnetic field generated by a second magnetic field generator may covera second end of the shell material source. Of course, it will beunderstood that additional magnetic field generators 80 (e.g. thirdmagnetic field generator, fourth magnetic field generator etc.) may beused in combination or separately with one or more shell materialsources 36, 38, 50 in order to exert a force on the nanoparticles movingthrough the shell material source, and dependent on the control andnumber of layered shells required.

Each of the magnetic field generators or sub-generators may work incollaboration, through a computer, to control magnetic nanoparticlesmoving through the shell material source to coat the magnetic corenanoparticles, or previously coated core-shell nanoparticles, with alayer of the shell material to specified dimensions, e.g. thickness.

Process

An apparatus, such as the apparatus described above, may be used tomanufacture an enhanced magnetic structure.

Matrix material and magnetic nanoparticles may be deposited on thesubstrate by operation of a matrix material source and a nanoparticlesource respectively. The matrix material and the nanoparticles may bedeposited simultaneously, for example by simultaneous operation of thetwo sources. The source of matrix material may be provided by anysuitable process or apparatus, including, for example, a thermalevaporator, such as a Molecular Beam Epitaxy (MBE) apparatus, asputtering apparatus, a laser ablation apparatus or an arc apparatus.The nanoparticle source may be provided by any suitable process orapparatus, including, for example a thermal gas aggregation apparatus, asputtering apparatus, a laser ablation apparatus, or an arc apparatus.

Deposition of the magnetic nanoparticles by way of vacuum assisteddeposition of magnetic nanoparticles in the gas phase and morespecifically by way of deposition of a beam of gas-phase magneticnanoparticles, comprises causing a beam of magnetic nanoparticles toimpinge upon the matrix as the matrix forms. The beam may be generatedby any suitable source, such as a gas phase source, a cluster beamsource, such as a gas aggregation source, a sputtering source, or alaser ablation source or an arc source. The gas phase source may beoperative to produce a beam of particle cores absent their shell layer.

Deposition of the shell layer may be by vacuum assisted deposition ofshell material vapour. Shell material vapour may therefore be providedin the same vacuum as a source of nanoparticle cores. The shell materialvapour may be generated by a thermal source, for example a thermalevaporator (such as an MBE source) or by sputtering, by laser ablation,or by an arc process. The temperature of a thermal source ofnanoparticles may be determined by the shell material to be deposited,e.g. 800° C. for silver and 1000° C. for iron. Any gases used in thecomposition may be introduced at low pressure.

Using known apparatus and processes, the time the core nanoparticlesspend in the shell deposition chamber or source is limited and isprimarily controlled by the pressure difference caused by the vacuumpump, thus there is limited control of the shell layer.

However, as noted above, the known apparatus is modified to comprise oneor more magnetic field generators. In the manufacture of magneticcore-shell nanoparticles, deposition of each shell layer may be byvacuum assisted deposition from a thermal evaporator as described above.

The magnetic field generator is activated to generate a magnetic fieldprior to the beam of nanoparticles entering the shell material source,or just as the beam of nanoparticles enters the shell material source.As the nanoparticles comprise a magnetic material, the magnetic fieldexerts a force on the nanoparticles. The strength and direction of themagnetic field is controlled in order to direct the nanoparticles.

For example, the magnetic force experienced by the nanoparticlesresulting from the magnetic field may act to reduce the speed of thenanoparticles, thereby causing them to spend a longer period of time inthe shell material source. The force may act to increase the speed ofthe nanoparticles, thereby causing them to spend a shorter period oftime in the shell material source. The force may act to deflect thenanoparticles in a direction having a component which is perpendicularto a path passing through the bore of the shell material source, therebycausing them to pass through the shell material source closer to theshell material itself. The force may act to rotate the nanoparticles asthey pass through the shell material source. The force may act to holdthe nanoparticles stationary or substantially stationary within theshell material source for a certain length of time.

By using the magnetic force to control the nanoparticles while they arewithin the shell material source, the user may exercise greater controlover the shell coating applied to the nanoparticles. For example, ifmore time is spent in the shell material source or the nanoparticlespass closer to the shell material itself, a thicker coating of shellmaterial will be applied to the nanoparticles. If the nanoparticles arerotated as they pass through the shell material source, a more uniformlayer of shell material will be deposited on the nanoparticles. If theposition of the nanoparticles is translated to move closer to the sourceof the shell material on one side (without rotation), an asymmetricalcoating may be applied.

Control of the magnetic field generator and therefore of the coatingapplied to the nanoparticles may be assisted by use of a computer. Asequence of different field generations may be programmed in order tocontrol the nanoparticles in a series of movements to result in themanufacture of nanoparticles with particular dimensions.

As will be understood from the foregoing, the nanoparticles source 34may produce a continuous stream of nanoparticles while in operation. Thenanoparticles may be slowed down on entering the shell material source,so that they travel relatively slowly through the shell material source,and the nanoparticles may optionally also be accelerated as they leavethe shell material source. Alternatively, or in addition, thenanoparticles may be deflected in a transverse direction having acomponent that is perpendicular to the main axis of the shell materialsource. A combination of such movements may be caused to take place bythe magnetic field generator, such as movement (possibly oscillatingmovement) back and forth in the transverse direction, or a movement in aspiral or helical path through the shell material source. However, insuch embodiments a continuous or substantially continuous stream ofnanoparticles may pass through the shell material source from thenanoparticle source 34.

In other embodiments, as the nanoparticles pass through the shellmaterial source, the movement of the nanoparticles may be controlled bythe field generated by the magnetic field generator so that thenanoparticles are held by the magnetic field in a stationary orsubstantially stationary position. Accordingly, nanoparticles willaccumulate in the shell material source until they are released by themagnetic field (e.g. by being accelerated towards the substrate 44). Theresult is “batches” of processed nanoparticles which may then proceed tosubsequent stages of processing or for deposition on the substrate. Insuch an approach, the nanoparticle source 34 may be controlled toproduce pulses or batches of nanoparticles, or alternatively thenanoparticle source 34 may produce a continuous stream of nanoparticles.The magnetic field generator 80 may also operate in a “pulsed” manner(i.e. produce one or more magnetic fields which vary over time,throughout the production of one “batch”, in a pattern that may then berepeated for a subsequent batch) in order to produce batches ofnanoparticles.

For simplicity only one magnetic field generator has been described. Asnoted above, magnetic field generators may be used in connection witheach shell coating stage. Furthermore, a series of generators may beused together, or generators may comprise one or more sub-generatorswhich are located orthogonally to each other to control movement inthree dimensions.

According to one example, only one layer of material is deposited on thenanoparticles. As stated above, the second shell material source 38 ofFIG. 2 is therefore either absent or inoperative. The matrix materialsource 34 generates a beam of nanoparticles of diameters in the range of0.5 nm to 5 nm. The diameter of the nanoparticles is determined bycontrolling the operating conditions of the matrix material source 34,for example the power level and the gas pressure therein. The beam ofnanoparticles passes through the bore of the first shell material source36 which comprises a tube 52 of a shell material, for example either Coor Ag and the movement of the nanoparticles is controlled by a magneticfield generated by the magnetic field generator 80. Each nanoparticle isthereby coated with a layer of the shell material to a thickness ofbetween 1 and 10 atomic layers. The operating conditions of the firstshell material source 36 are determined by the material to be deposited,and the required thickness of the shell layer concerned. For example, inthe case of a thermal evaporator, the operating temperature for Ag isabout 800° C.

If it is desired to increase the range of thicknesses of the shell layerthe operating temperature need only be increased slightly because vapourpressure is very sensitive to temperature. For example, to double thethickness of an Ag layer it is only necessary to increase thetemperature by about 50° C. Alternatively, the speed of thenanoparticles may be decreased. If it is desired to produce a moreuniform layer, the nanoparticles are caused to rotate. In order to ‘finetune’ the dimension of the shell layer, the magnetic field generation isadjusted.

In this example, the matrix material source 32 operates at the same timeas the nanoparticle source 34 to generate a beam of matrix material, forexample Co or Ag, such that the matrix material beam is of the samematerial as the coating on the nanoparticles. The matrix material beamand the beam of nanoparticles are deposited simultaneously on thesubstrate 44 to form a magnetic structure comprising a matrix in whichnanoparticles are embedded.

Each magnetic nanoparticle may comprise a plurality of shell layers overthe core. The shell layers may be of the same material as each other orone another or different material to each other or one another. Theprocess may therefore comprise a deposition step for each shell layer.

Alternatively, different shell materials may require differentdeposition techniques, and each may be provided. The plural shellmaterial sources may be disposed in line whereby, for example, a firstsource provides for deposition of a first shell layer and a secondsource provides for deposition of a second shell layer over the firstshell layer. Subsequent shell layers may be deposited on the previousshell layer by respective sources.

For simplicity, and for comparison with known systems, the process ofmanufacturing the desired nanoparticles has been described as beingdeposited on a substrate once the processing steps to coat thenanoparticles have been completed. It is not necessary that theprocessed nanoparticles are deposited on a substrate. Instead, thenanoparticles may be collated and kept, for example, in a solution. Theneed to deposited the processed nanoparticles on a substrate or collatedand kept in another way will depend on the ultimate purpose orsubsequent proceeding required.

Again, for simplicity and for comparison with known systems, theforegoing has described a co-deposition process with a matrix. The useof a matrix material is independent from the processing of thenanoparticles. Accordingly, it is not necessary to use a matrix materialin deposition on a substrate nor use a matrix material with othermethods of collating the processed nanoparticles.

Product

If required, the matrix material may be a single element, an alloy ofmore than one element, or a combination thereof. The single element,alloy or combination may include embedded gas atoms and/or molecules.The matrix material may be a metal and, more specifically, one of atransition metal and a rare earth metal, or an alloy containing atransition metal and/or a rare earth metal, and may include embedded gasatoms and/or molecules.

Core-shell nanoparticles are nanoparticles having a core of a corematerial and a shell layer covering the core, the shell layer being ofshell material, different to the core material. A core-shellnanoparticle may be provided with more than one shell layer. The corematerial may be a single element, an alloy of more than one element, ora combination thereof. The single element, alloy or combination mayinclude embedded gas atoms and/or molecules. The shell layer materialmay be a single element, an alloy of more than one element, or acombination thereof. The single element, alloy or combination mayinclude embedded gas atoms and/or molecules.

Each core-shell magnetic nanoparticle may comprise a core formed from amagnetic transition metal and a shell layer of either a magnetic ornonmagnetic transition metal. The nonmagnetic transition metal may be aGroup 11 metal such as gold or silver. Thus, examples of core/shelllayer composition may be Fe/Co Co/Fe, Fe/Ag, Co/Ag, Fe/Au or Co/Au.

A surface of the shell layer may define an exterior surface of themagnetic nanoparticle and therefore the diameter of the nanoparticle.

In a deposited material, where used the matrix material may be of thesame material as the shell layer. For example, each magneticnanoparticle may comprise a Fe core covered at least in part with alayer of Co and the matrix material may be Co. By way of furtherexample, each magnetic nanoparticle may comprise a Co core covered atleast in part with a layer of Au and the matrix material may be Au. Useof the same material may reduce the likelihood of the particle corescoming into contact even at volume fractions much higher than thepercolation threshold.

Each magnetic nanoparticle, for example, may have a diameter notexceeding around 10 nm, although the nanoparticles could be between 0.5nm and 50 nm. The magnetic moment per atom of magnetic nanoparticles ofsmaller diameters has been found to be significantly higher comparedwith bulk structures formed from the same material. For higher magneticmoment, each magnetic nanoparticle may therefore have a diametersubstantially in the range 0.5 nm to 5 nm.

In examples of core-shell nanoparticles, the shell layer may have athickness of between around 0.2 nm and 4 nm as may be achieved fromknown methods, also. However, with known methods it is unlikely that thelayer will be complete, i.e. there may be gaps such at the covering ofthe core is less than 90% complete. According to the apparatus andmethods/processes disclosed herein, it is possible to achieve completeor total covering of the core, i.e. 100% complete. For example,considering a batch of 100 nanoparticles, the average of the percentagecoating of individual nanoparticles will be at least 90%.

In other examples, making use of the apparatus and process disclosedherein, the shell layer may have a specified thickness of more than 4 nmand could be significantly higher. For some applications between 2 nmand 20 nm has been found to be useful. In terms of atomic layers, thethickness of the shell layer may be between 1 and 10 atomic layers orgreater than 10 atomic layers using the apparatus and process disclosedherein. The diameter of the core and the thickness of the shell layermay be determined independently from one another. The diameter of thecore and the thickness of the shell layer may be specified by theapplication of and requirements for the nanoparticles.

An exemplary structured nanoparticle is shown schematically in FIG. 4which shows a perspective view of a Co core coated with a layer of eachof Cr and a rare earth metal (i.e. Ho or Dy). FIG. 4 also shows asection through a coated nanoparticle 70 with Co forming the core 72, Crforming a layer immediately over the Co core and either Ho or Dy formingan exterior layer immediately over the Cr layer. FIG. 4 further shows abeam of nanoparticles 78 after deposition of the Cr layer and Ho or Dylayer. The matrix material source 32 is operative at the same time asthe nanoparticle source 34 to generate a matrix material beam of eitherHo or Dy such that the beam is of the same material as the outer coatingon the Co nanoparticles. The matrix material beam and the beam ofnanoparticles are deposited simultaneously on the substrate 44 to form amagnetic structure comprising a matrix in which nanoparticles areembedded.

A magnetic structure may thereby be formed in which magnetic core-shellnanoparticles are distributed through and embedded in the matrixmaterial. The magnetic structure is typically formed as a thin film onthe substrate. The deposited thin film can be used in variousapplications or further processed as needed in the ultimate application.However, as discussed above, deposition on a substrate is not essential,nor is the use of a matrix material.

Structured Nanoparticles

Structured nanoparticles refer to structures constructed from aplurality of nanoparticles. The plurality of nanoparticles which make upa structured nanoparticles may comprise simple nanoparticles, core-shellnanoparticles, multishell nanoparticles or any combination thereof.

As will be appreciated from the foregoing, magnetic (simple or coreonly) nanoparticles or magnetic core-shell nanoparticles may bemanipulated individually using controllable magnetic fields.

A plurality of nanoparticles may be used as ‘building blocks’ to createa structure. Structures may be constructions from simple, core-shell ormultishell nanoparticles. In order to make the ‘blocks’ ‘stick’ to eachother, they may be magnetised. In order to break apart the ‘blocks’ theymay be de-magnetised.

By controlling individual or groups/batches of nanoparticles in themagnetic field, it is possible to move them into position to form astructure. Thus, it is possible to build a variety of formations usingnanoparticles as building blocks.

One or more magnetic field generators may be used to create a magneticfield to act on magnetic nanoparticles before they are deposited on asubstrate. As with use in conjunction with a shell material source, themagnetic field may be generated by more than one magnetic fieldgenerator(s) which are used in collaboration to provide a controllingforce on nanoparticles which enter the field. The magnetic fieldgenerator(s) may be used, together with a computer, for specific timeperiods and to cause specific translational and rotational movements ofnanoparticles. Thus, a program can be used to cause a series ofmovements to create nanoparticle structures in a building phase.

For structured nanoparticles, the core may be of a magnetic material.The core material may be a single element, an alloy of more than oneelement, or a combination thereof. The single element, alloy orcombination may include embedded gas atoms and/or molecules. Morespecifically the magnetic material may be a magnetic transition metal,such as one of Fe, Co and Ni.

For structured magnetic nanoparticles, the magnetic nanoparticles i.e.the core nanoparticles, may be at least in part covered with a shelllayer of material. Typically the shell material is different to that ofthe core and reduces the likelihood of cores coming into contact witheach other when deposited on the substrate.

The building phase or process can be used in serieswith coatingnanoparticles. Nanoparticles may be coated individually, before enteringthe building phase. Alternatively, nanoparticle structures may be coatedafter the building phase. Further, a combination of coated and uncoatednanoparticles may be used. Still further, nanoparticles may receive oneor more coating layers, then enter a building phase, and subsequentlyreceive one or more additional coating layers. Finally the structuresmay be deposited on a substrate, with or without a matrix material.

In one example, the nanoparticles may be formed into a formation whichcomprises an external structure which at least partially surrounds aninternal space, such as a cube formation, a pyramid formation, or apolyhedron formation, for use as a container. Other material may betrapped inside the internal space of the formations. If and when thecontained material is required to be released, the container may becollapsed by de-magnetising the structure, thus releasing the containedmaterial.

Uses

The form of the structured magnetic nanoparticles depends on theirintended use.

As disclosed in GB2510228B, magnetic structures as produced anddescribed may be used to form a write head for use in a device. The moreaccurate control of the shell layer(s) allows for improved tolerancesand performance of an electromagnetic data storage device.

Structured magnetic nanoparticles may also be used in other hard diskdrive (HDD) applications.

Magnetic nanoparticles may also be useful in medical applications andproducts for human consumption, for example, for the delivery ofmaterials (e.g. drugs) to specific locations in the body. Structuredmagnetic nanoparticles may be particularly useful in these applications.

For example, nanoparticles which are coated in Ag, alumina or othernoble metal are medically inert. Therefore, the nanoparticles can besafely used to deliver magnetic material to specific locations in thebody. Other combinations of core-shell may also be suitable forparticular medical treatments. For example, Fe-core FeO-shellnanoparticles may be incorporated in a water-dispersible powdercomprising grains of matrix material embedded with one or morenanoparticles. The powder may be produced by depositing a thin film ofmatrix-nanoparticle material, where the nanoparticles are Fe-coreFeO-shell material. The film is subsequently processed to produce grainsof matrix material embedded with the nanoparticles. Alternatively,rather than depositing the nanoparticle material on a substrate, thenanoparticles are collated and kept in solution.

Other treatments may require a high concentration of magnetic materialto be delivered in a specific location, and with no danger ofpercolation, such as in the treatment of tumours. Coated nanoparticlesare particularly useful in controlling the percolation level.

As disclosed in GB2537777A, coated nanoparticles may be used incosmetics.

Other applications include use in motors, generators or turbines. Forexample, using a deposited film of magnetic nanoparticles to producelaminate or coiled material. The films are arranged in a laminatedstructure and pressed to produce a rotor or stator for use in electricmachines. In particular, this application benefits from increasedmagnetic moment due to the reduced percolation rate of coatednanoparticles.

Further, a combination of techniques may be used to improve somesystems. For example, in MRI imaging, a laminated structure ofnanoparticle films, similar to those that could be used to producerotors or stators, could be used to improve the magnetic density of themagnetic core. Further, a magnetic nanoparticle solution may beadministered to a patient, prior to being scanned by the MRI machine.The nanoparticle solution acts as a contrast enhancer to improvedetection of internal structures being imaged. Each techniqueindependently improves the contrast and therefore data collection fromthe scan.

As will be appreciated, by better controlling the deposition of shellmaterial on a shell-core nanoparticle structure, it is possible tobetter control specific properties of nanoparticles.

When used in this specification and claims, the terms “comprises” and“comprising” and variations thereof mean that the specified features,steps or integers are included. The terms are not to be interpreted toexclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the followingclaims, or the accompanying drawings, expressed in their specific formsor in terms of a means for performing the disclosed function, or amethod or process for attaining the disclosed result, as appropriate,may, separately, or in any combination of such features, be utilised forrealising the invention in diverse forms thereof.

1-17. (canceled)
 18. An apparatus for forming structured nanoparticles,comprising: a magnetic nanoparticle source operable to generate a beamof magnetic nanoparticles; and at least one controllable magnetic fieldgenerator operable to generate a magnetic field through which the beamof magnetic nanoparticles pass; whereby magnetic nanoparticles withinthe beam of magnetic nanoparticles passing through the controllablemagnetic field are arranged into structured nanoparticles.
 19. Theapparatus of claim 18, further comprising: at least one shell materialsource comprising a bore through which the beam of magneticnanoparticles pass to coat the structured nanoparticles.
 20. A method ofmanufacturing structured nanoparticles, comprising: generating a beam ofmagnetic nanoparticles from a source of magnetic nanoparticles source;passing the generated magnetic nanoparticles through a magnetic fieldgenerated by a controllable magnetic field generator; wherein magneticnanoparticles within the beam of magnetic nanoparticles passing throughthe magnetic field build structured nanoparticles.
 21. The method ofclaim 20, further comprising: depositing the structured nanoparticles ona substrate.
 22. The method of claim 20, further comprising: collatingthe structured nanoparticles in a solution.
 23. A core-shell magneticnanoparticle structure, comprising: a nanoparticle having a magneticcore; and at least one shell layer around the magnetic core having athickness between 0.2 nm and 4 nm, wherein the at least one shell layerprovides a coating of at least a 90% of the magnetic core.
 24. Thecore-shell magnetic nanoparticle structure of claim 23, wherein the atleast one shell layer completely coats the magnetic core.
 25. Thecore-shell magnetic nanoparticle structure of claim 23, wherein anaverage of the coating of the magnetic core of the nanoparticles withina group of at least 100 of the nanoparticles is at least 90%. 26.(canceled)
 27. (canceled)
 28. (canceled)
 29. (canceled)